1. Field of the Invention
The present invention relates to an improved solar energy collection system.
2. Description of the Prior Art
The number of solar energy collection systems in the marketplace has increased rapidly in the last few years. This increased has been due principally to two major reasons. One is that the underlying technical knowledge of solar energy collection has increased. Further, the rising costs of fossil fuels such as oil and natural gas has generated a need for alternative energy sources.
One of the standard solar energy collection systems on the market today is the flat-plate collector. Conventional flat-plate collectors are generally comprised of a black-coated solar energy absorber plate which is backed by a heat insulative base and protected from the ambient atmosphere by one or more layers of transparent covers. In operation, solar radiation is transmitted through the transparent covers and absorbed by the black surface into the absorber plate. The absorbed solar radiation is thereby converted into thermal energy, which is removed from the resulting heated absorber plate by air, water or other suitable heat transfer fluids which function in a heat exchanging relationship with the heated plate. The resulting heated transfer fluid can be then used for such beneficial purposes such as heating, refrigeration or electric-power generation.
Unfortunately, the flat-plate solar energy collection systems as presently known generally do not provide highly efficient energy collection. When solar radiation is converted to thermal energy on the absorber plate, not all of the resulting thermal energy can be removed by the heat transfer fluid and then be utilized in some useful form. Instead, a large amount of the thermal energy is re-radiated and lost into the ambient atmosphere through the air space between the transparent cover or covers and the absorber plate. Furthermore, large amounts of thermal energy will also leave the absorber plate and be lost by means of conduction and convection.
In the past, many attemps have been made to reudce such heat losses. For example, it has been urged that heat losses by conduction and convection may be minimized by employing multi-transparent covers and/or a vacuum in the overlying space. Further, it has been suggested that re-radiation of the thermal energy can be reduced by coating the transparent covers with special paints or films which allow a high transmittance of solar radiation to the absorber but prevent the thermal radiation of the absorber plate from being re-radiated through the transparent cover. See U.S. Pat. No. 3,957,029, issued to Nozik et. al. on May 18, 1976. It has been suggested that the re-radiation can also be reduced by filling the space with glass fibers. See U.S. Pat. No. 4,015,582, issued to Liu et. al. on Apr. 5, 1977. Still further, it has been suggested that special black paints or plating be used to coat the absorber plate in order to increase its absorbability and lower its reflectivity. See Chemical Week, Sept. 2, 1977, pp. 54, 56, and 58. However, these approaches do not appear to be totally satisfactory because of the efficiency of the presently known solar energy collection systems have not been raised sufficiently to justify the added costs of such improvements and/or to make such system useful for a wide degree of applications. Thus, there is still a need in the art for a simple solution to improve the relatively low efficiency of solar collectors. The present invention presents such a solution.